What is Cystinuria?
Cystinuria is a medical condition that causes stones in the kidneys. These are not like ‘common’ kidney stones; people with cystinuria have stones that are larger, harder to treat and come back much more frequently than common stones. These stones can block the flow of urine between the kidney and bladder, causing severe pain in the back and sides, blood in the urine and infection in the kidneys. This is a genetic condition, caused by a fault in the genes of people with cystinuria. Sometimes cystinuria can run in families (the faulty gene is inherited) or people can be affected with no history of any family previously having cystinuria stones (they developed a new fault when they were conceived). Children and adults can be affected; the usual age of a first stone is in the mid-20’s – but this is very variable. Children under 10 and adults over 60 have been reported in the medical literature having their first cystine kidney stone. Cystinuria is a rare condition (sometimes known as an ‘Orphan Disease’) and affects about 1 in 7 000 people – this means there are about 8 000 people in the UK making cystine stones and living with the challenges of this condition.
The genetic fault (sometimes called a ‘mutation’ or ‘defect’) causes the kidney to lose lots of amino acids into the urine (amino acids are small parts of protein). Normally these amino acids are kept back in the blood and circulation by the kidneys, but in someone with cystinuria the amino acid ‘pump’ in kidney cells (also known as a ‘transporter’) does not work properly and the urine has large quantities of amino acids. One of these amino acids, cystine, when it is in solution at a high concentration, forms crystals (just like growing blue copper sulphate crystals in a jam jar!). These grow in the kidneys, until they get to a size that causes urine blockage and pain.
The pain from kidney stones can be severe, needing strong pain-killing medication, or a visit to hospital for treatment. Sometimes small kidney stones can be passed out in the urine when someone pees, but often surgery is needed to remove the stones. If the urine flow is blocked for a time, infection can build up in the kidney, making the patient feel very unwell and needing more treatment. Shock-wave therapy is often used to treat ‘common’ stones, but stones made from cystine are resistant to shock-waves and surgery is needed to remove them. Repeating episodes of urine blockage, infection and surgery can cause the kidneys to become permanently damaged.
There are medical treatments and steps that people with cystinuria can take to reduce the number of crystal stones that form in their kidneys. Anyone with cystinuria needs to talk about treatment options with their specialist kidney doctor, and not start or change treatment without discussing it with them first. One of the most important changes someone with cystinuria can make to their diet is to drink more water – 3 to 5 litres of water in addition to their normal diet. As you drink more water, and the amount of urine you make increases, this makes the cystine more dilute – and makes it less likely that crystal stones will form. This simple step is very successful for some people, but having to remember to carry water around and perhaps have more visits to a toilet can be disruptive to everyday life, school and work. The chemistry of crystals means that making the urine more alkali (the opposite of acidic) also makes is less likely that cystine stones will form and grow. People with cystinuria can take bicarbonate medications that makes the urine alkali – this is effective for some people, but there can be side effects of some bloating or nausea. There are two medical drug treatments available in the UK: d-penicillamine and alpha-MPG. These tablet medications both work in the same way by sticking to cystine in the bloodstream and reducing the amount of cystine in the urine – and making it less likely that stones will form. Again, these medications can be really helpful for some people, but others can have a range of significant side effects, such as skin rashes, blood, kidney and liver changes. This means that some people will have to stop taking their medication. It is important that patients are monitored closely by their doctor if they are taking either of these two treatments.